1. Field of the Invention
The present invention relates to a redundancy relieving circuit suitable for use in a semiconductor memory device such as a Dynamic Random Access Memory (DRAM), which is capable of obtaining a stable operation even at a high frequency.
2. Description of the Related Art
A semiconductor memory device has lattice-like wiring structures called “memory cell arrays” comprising a plurality of word lines extending in a horizontal direction and a plurality of bit lines extending in a vertical direction. Storing elements are respectively provided at points where the word lines and the bit lines intersect. They are operated by the word lines and the bit lines.
On the other hand, when a large-capacity semiconductor memory device is mass-produced, it is difficult to manufacture it without any trouble in respective bit lines because a large number of the bit lines exist within the semiconductor memory device. Therefore, spare bit lines are placed in parallel with other bit lines in advance in preparation for the occurrence of trouble in the bit lines. If trouble occurs in a bit line, a circuit is then changed in such a manner that the bit line having caused the trouble is not used, and a spare bit line is used instead. Cutting a fuse disposed within the circuit in advance performs such a circuit change. Thus, the yield of production of the semiconductor memory device is prevented from being reduced. This has been described in a patent document 1 (Japanese Unexamined Patent Publication No. 2000-48589).
The number of bit lines lying within a semiconductor memory device is increasing or building up rapidly with a recent increase in the capacity of the semiconductor memory device. With its increase, the number of fuses corresponding to the respective bit lines also increases. Since the fuses are high in resistance as compared with a normal wiring, the resistance of a wiring to which a large number of fuses are connected in series, increases. Therefore, a signal inputted to such a wiring is not immediately transferred. Thus, a problem arises in that adaptation to a high frequency operation becomes difficult.